Boron-promoted reducible metal oxides and methods of their use

ABSTRACT

Compositions comprising boron-promoted reducible metal oxides (expecially reducible oxides of Mn) and optionally containing alkali and alkaline earth metal components are disclosed, as well as use thereof for hydrocarbon conversions characterized by formation of by-product water. Particular processes comprise the conversion of methane to higher hydrocarbons and the dehydrogenation of dehydrogenatable hydrocarbons, e.g., dehydrogenation of C 2  -C 5  alkanes to form the corresponding olefins.

This is a divisional of co-pending application Ser. No. 877,574, filedon June 23, 1986, now U.S. Pat. No. 4,777,313, which is acontinuation-in-part of U.S. patent application Ser. No. 06/683,296filed Dec. 18, 1984 (now abandoned), which in turn is acontinuation-in-part of the following U.S. patent applications: (1) Ser.No. 06/522,937 filed Aug. 12, 1983 (now U.S. Pat. No. 4,499,322); (2)Ser. No. 06/522,936 filed Aug. 12, 1983; (now U.S. Pat. No. 4,495,374);(3) Ser. No. 06/600,654 filed Apr. 16, 1984 ((now U.S. Pat. No.4,547,611), and Ser. No. 06/600,655 filed Apr. 16, 1984 (now abandoned),both of which are in turn continuations-in-part of Ser. No. 06/522,937filed Aug. 12, 1983 and of Ser. No. 06/522,936 filed Aug. 12, 1983.

BACKGROUND OF THE INVENTION

This invention relates to hydrocarbon conversion processes employingreducible metal oxide compositions. One particular application of thisinvention is a method for converting methane to higher hydrocarbons.Another particular application of this invention is a process for theoxidative dehydrogenation of hydrocarbons, especially a process for theoxidative dehydrogenation of paraffinic hydrocarbons to thecorresponding mono-olefins.

A central aspect of the presently claimed invention is the catalystcomposition employed in such hydrocarbon conversion processes. In oneparticular aspect, the present invention relates to compositionscomprising alkaline earth promoted reducible metal oxides (especiallyreducible oxides of manganese). In one still more specific embodiment,this invention relates to compositions comprising oxides of Mn, alkalineearth metals, alkali metals and boron.

Recently, it has been discovered that methane may be converted to higherhydrocarbons by a process which comprises contacting methane and anoxidative synthesizing agent at synthesizing conditions (e.g., at atemperature selected within the range from about 500° to about 1000°C.). Oxidative synthesizing agents are compositions having as aprincipal component at least one oxide of at least one metal whichcompositions produce C₂ + hydrocarbon products, co-product water, and acomposition comprising a reduced metal oxide when contacted withmembrane at synthesizing conditions. Reducible oxides of several metalshave been identified which are capable of converting methane to higherhydrocarbons. In particular, oxides of manganese, tin, indium,germanium, lead, antimony, bismuth, praseodymium, terbium, cerium, ironand ruthenium are most useful. See commonly-assigned U.S. Pat. Nos.4,443,649 (Mn); 4,444,984 (Sn); 4,445,648 (In); 4,443,645 (Ge);4,443,674 (Pb); 4,443,646 (Bi); 4,499,323 (Pr); 4,499,324 (Ce); and4,593,139 (Ru), the entire contents of which are incorporated herein byreference. See also commonly-assigned U.S. patent application Ser. No.06/666,694 (Fe) the entire content of which is incorporated herein byreference.

Commonly-assigned U.S. Pat. No. 4,554,395 discloses and claims a processwhich comprises contacting methane with an oxidative synthesizing agentunder elevated pressure (2-100 atmospheres) to produce greater amountsof C₃ ⁺ hydrocarbon products.

Commonly-assigned U.S. Pat. No. 4,560,821 discloses and claims a processfor the conversion of methane to higher hydrocarbons which comprisescontacting methane with particles comprising an oxidative synthesizingagent which particles recirculate between two physically separatezones--a methane contact zone and an oxygen contact zone.

As noted, the reaction products of such processes are mainly ethylene,ethane, other light hydrocarbons, carbon oxides, coke and water. Itwould be beneficial to these oxidative synthesis processes to reduceselectivities to carbon oxides and coke.

Hydrocarbon conversion processes employing the composition of thisinvention are characterized by relatively severe reaction conditions andby the formation of coproduct water. Thus, hydrothermal stability atelevated temperatures (e.g., 500° to 1000° C.) is an important criterionfor the compositions. Moreover, uses contemplated for the presentcompositions require catalysts which are rugged, attrition-resistant,and stable at high temperatures. It is also desirable that thecompositions are able to operate effectively for relatively long periodswhile cycling between oxidized and reduced states.

An object of the present invention is a composition and process forhydrocarbon conversion processes, especially for processes characterizedby the formation of byproduct water. A related object is a rugged,stable, attrition-resistant oxidant composition for such processes.

Another object of the present invention is a composition and process forconverting methane to higher hydrocarbons, especially for processescharacterized by the formation of byproduct water. A related object is arugged, stable, attrition-resistant oxidant composition for such methaneconversion process.

Still another object of the present invention is a composition andprocess for the oxidative dehydrogenation of hydrocarbons. A relatedobject is a rugged, stable, attrition-resistant oxidant composition forsuch processes. Another related object is a composition and process forthe oxidative dehydrogenation of paraffinic hydrocarbons to form thecorresponding mono-olefins.

Other objects, aspects and advantages of the invention will be apparentto those skilled in the art upon studying the specification and theappended claims.

SUMMARY OF THE INVENTION

It has now been found that hydrocarbon conversions (especially theconversion of methane to higher hydrocarbons) wherein a hydrocarbon feedis contacted at elevated temperatures with a solid comprising areducible metal oxide is improved when the contacting is conducted inthe presence of a promoting amount of at least one member of the groupconsisting of boron and compounds thereof. Examples of reducible metaloxides are oxides of Mn, Sn, In, Ge, Pb, Sb, Bi, Pr, Tb, Ce, Fe and Ru.However, distinct embodiments of the present invention are directedtoward processes and catalyst compositions comprising reducible oxidesof Mn. In certain embodiments of this invention, the catalystcompositions are characterized by the substantial absence ofcatalytically effective iron, to distinguish known oxidativedehydrogenation catalysts based on the use of Mn ferrites.

One class of catalyst compositions useful in the process of thisinvention comprises:

(1) at least one reducible metal oxide,

(2) at least one member of the group consisting of boron and compoundsthereof, and

(3) at least one member of the group consisting of oxides of alkalineearth metals.

A related class of catalyst compositions further comprises at least onealkali metal or compound thereof.

Alkali metals are selected from the group consisting of lithium, sodium,potassium, rubidium and cesium. Lithium, sodium and potassium, andespecially lithium and sodium, are preferred alkali metals.

Alkaline earth metals are selected from the group consisting ofmagnesium, calcium, strontium and barium. Presently preferred members ofthis group are magnesium and calcium. Compositions derived from magnesiahave been found to be particularly effective catalytic materials.

Further classes of catalysts compositions within the scope of thisinvention are mixed oxides of sodium, magnesium, manganese and boroncharacterized by the presence of the crystalline compound NaB₂ Mg₄ Mn₂O_(w) wherein x is the number of oxygen atoms required by the valencestates of the other elements, said compound having a distinguishingx-ray diffraction pattern. In its most active form, the compound isbelieved to correspond to the formula NaB₂ Mg₄ Mn₂ O₁₁. While thiscrystalline compound has been found to be associated with highlyeffective oxidant compositions, it has further been found that stillbetter results are obtained when the oxidant is characterized by both:(1) the presence of crystalline compound NaB₂ Mg₄ Mn₂ O_(x) and (2) astoichiometric excess of of Mn relative to at least one of the otherelements of the crystalline compound. In currently preferred oxidants ofthis type, a stoichiometric excess of Mn relative to B is provided. In astill more specific preferred embodiment excess amounts of Na and Mg, aswell as Mn, are present in the mixed oxide composition relative to theamounts required by the amount of boron present to satisfy thestoichiometry of the compound NaB₂ Mg₄ Mn₂ O_(x).

The compositions of this invention are useful in a variety ofhydrocarbon conversion processes. When the active form of thecomposition (i.e., the composition in an oxidized state) is contactedwith methane at elevated temperatures (e.g., at temperatures within therange of about 500° to 1000° C.), methane is converted to higherhydrocarbon products. The compositions are also effective contact agents(i.e., catalysts) in oxidative dehydrogenation processes.

DETAILED DESCRIPTION OF THE INVENTION

While the composition of the present invention is referred to as a"catalyst", it will be understood that, under conditions of use, itserves as a selective oxidant, and, therefore, takes on thecharacteristics of a reactant during use. Thus, for example, the term"Mn-containing oxides" is meant to embrace both reducible oxides of Mnand reduced oxides of Mn, it being understood reducible oxides comprisethe principal active component of the compositions.

Consider the requirements of the oxidant. For selective reaction to takeplace, the oxidant must release the proper quantity of oxygen in thereaction zone within the proper period of time. If this does not occur,either non-selective oxidation reactions result (forming CO_(x)), or thedegree of conversion is restricted. Furthermore, the oxidant must becapable of being repeatedly regenerated. Minimal or no coke formation isdesirable. The oxidant must exhibit long life; the oxidant must exhibitrelatively constant performance over the time while sequentially: (1)achieving selective conversion of reactants and (2) being regenerated toits active state. Mechanisms for the acquisition and release of oxygenby the oxidant are not fully understood. Undoubtedly, both physical andchemical phenomena are invloved. For example, the oxygen may be bothphysically adsorbed and chemically reacted to form compounds of higheroxidation states.

In the following formulae describing the compositions of this invention,the relative number of oxygens is designated by "x". This x is variablebecause the compositions may continually gain and lose oxygen duringuse. Thus setting a strict range of values for x would be imprecise andpossibly misleading. Generally, the value ascribed to x falls within therange of the number of oxygens required in the higher oxidation states(the "active" or "oxidized" composition) to the number of oxygensrequired in the lower oxidation states (the "reduced" composition).

The catalysts of the present invention, in their active state, compriseat least one reducible oxide of at least one metal, which oxide whencontacted with methane (or higher hydrocarbons) at synthesizing (ordehydrogenation) conditions (e.g., at a temperature within the range ofabout 500° to 1000° C.) produces higher hydrocarbon products (or in thecase of higher hydrocarbon dehydrogenation, dehydrogenated hydrocarbonproducts), coproduct water, and a reduced metal oxide. The term"reducible" is used to identify those oxides of metals which are reducedunder the aforesaid conditions. The term "reducible oxides of metals"includes: (1) compounds described by the general formula M_(x) O_(y)wherein M is a metal and x and y designate the relative atomicproportions of metal and oxygen in the composition and/or (2) one ormore oxygen-containing metal compounds (i.e., compounds containingelements in addition to the metal and 0), provided that such oxides andcompounds have the capability of producing higher hydrocarbon productsfrom methane, or of producing dehydrogenated hydrocarbons fromdehydrogenatable hydrocarbons, as described herein.

Effective agents for the conversion of methane to higher hydrocarbonshave previously been found to comprise reducible oxides of metalsselected from the group consisting of manganese, tin, indium, germanium,antimony, lead, bismuth and mixtures thereof. See U.S. Pat. Nos.4,443,649; 4,444,984; 4,443,648; 4,443,645; 4,443,647; 4,443,644; and4,443,646.

Reducible oxides of cerium, praseodymium, and terbium have also beenfound to be effective for the conversion of methane to higherhydrocarbons, particularly associated with an alkali metal componentand/or an alkaline earth metal component. See U.S. Pat. Nos. 4,499,324(Ce) and 4,499,323 (Pr) and also see commonly-assigned U.S. patentapplication Ser. No. 06/600,918 (Tb).

Reducible oxides of iron and ruthenium are also effective, particularlywhen associated with an alkali or alkaline earth component. Seecommonly-assigned U.S. patent application Ser. No. 06/600,730 (Fe) andU.S. Pat. Nos. 4,489,215 and 4,593,139 (Ru).

One class of preferred compositions is characterized by the substantialabsence of catalytically effective Ni and the noble metals (e.g., Rh,Pd, Ag, Os, Ir, Pt and Au) and compounds thereof, to minimize thedeleterious catalytic effects of such metals and compounds thereof. Forexample, at the conditions (e.g., temperatures) under which the presentcompositions are used, these metals tend to promote coke formation andoxides of these metals tend to promote formation of combustion products(CO_(x)) rather than the desired hydrocarbons. The term "catalyticallyeffective" is used to identify that quantity of one or more of nickeland the noble metals and compounds thereof which, when present,substantially changes the distribution of products obtained whenemploying the compositions of this invention.

Other additives may be incorporated into the composition of thisinvention. For example, addition of a phosphorus component has beenfound to enhance the stability of the composition. When used, phosphorusmay be present up to an amount providing an atomic ratio of P to thereducible metal oxide component (expressed as the metal e.g., Mn) ofabout 2/1. If phosphorus is employed, it is desirable to provide itduring catalyst preparation in the form of phosphates of alkali metals(e.g., orthophosphates, metaphosphates and pyrophosphates).Pyrophosphates are preferred. Sodium pyrophosphate is particularlypreferred. P can be provided in other forms though. Examples includeorthophosphoric acid, ammonium phosphates and ammoniumhydrogenphosphates.

Further examples of other components which may be present in thecompositions of this invention are halogen and chalcogen components.Such components may be added either during preparation of the catalystsor during use. Methane conversion processes employing halogen-promoted,reducible metal oxides are disclosed in U.S. Pat. No. 4,544,784. Metalconversion processes employing chalcogen-promoted, reducible metaloxides are disclosed in U.S. Pat. No. 4,544,785.

CATALYST COMPOSITIONS

One broad class of compositions useful in the processes of thisinvention comprises:

(1) at least one reducible oxide of at least one metal which oxides whencontacted with methane at synthesizing conditions are reduced andproduce higher hydrocarbon products and water and

(2) at least one member selected from the group consisting of boron andcompounds thereof.

The relative amounts of the two components used to form the catalyst isnot narrowly critical. However, the preferred atomic ratio of thereducible metal oxide component (expressed as the metal, e.g., Mn) tothe boron component (expressed as B) is within the range of about0.1-20:1, more preferably within the range of about 0.5-5:1.

One narrower class of compositions useful in the processes of thisinvention comprises:

(1) at least one reducible metal oxide,

(2) at least one member of the group consisting of boron and compoundshereof, and

(3) at least one member of the group consisting of oxides of alkalineearth metals.

Preferred compositions contain more than about 10 wt. % of the alkaliearth component, more preferably they contain more than 20 wt. % of thealkaline earth component. Reducible metal oxides are preferably presentin an amount within the range of about 1 to 40 wt. % based on thecombined weight of the metal (e.g., Mn) and the alkaline earthcomponent, more preferably within the range of about 5 to 30 wt. %, andstill more preferably within the range of about 5 to 20 wt. %. Preferredcatalysts of this class are mixed oxide compositions satisfying thefollowing empirical formula:

    MB.sub.b C.sub.c O.sub.x

wherein M is the reducible metal component, B is boron, and C is thealkaline earth component and wherein b is within the range of about 0.1to 10, c is within the range of about 0.1 to 100, and x is the number ofoxygen atoms required by the valence states of the other elements.Preferably, b is within the range of about 0.1 to 4. Preferably, c iswithin the range of about 0.5 to 15, more preferably about 1 to 6.

A further class of compositions useful in the processes of thisinvention comprises:

(1) at least one reducible metal oxide,

(2) at least one alkali metal or compound thereof,

(3) at least one member of the group consisting of boron and compoundsthereof, and

(4) at least one member of the group consisting of oxides of alkalineearth metals.

Preferred catalysts of this class are mixed oxide compositionssatisfying the following empirical formula:

    MA.sub.a B.sub.b C.sub.c O.sub.x

wherein M is the reducible metal component, A is at least one alkalimetal, B is boron, C is at least one alkaline earth metal and wherein ais within the range of about 0.01 to 10, b is within the range of about0.1 to 20, c is within the range of about 0.1 to 100, and x is thenumber of oxygen atoms required by the valence states of the otherelements. Preferably b is within the range of about 0.1 to 10.Preferably, c is within the range of about 1 to 7.

A particularly preferred class of catalysts useful in the processes ofthis invention are mixed oxide compositions containing Na, Mg, Mn andboron which compositions are characterized by the presence of thecompound NaB₂ Mg₄ Mn₂ O_(x) wherein x is the number of oxygen atomsrequired by the valence states of the other elements present in thecompound. This compound possesses a definite, distinguishing crystallinestructure whose x-ray diffraction pattern is substantially as set forthin Table I. Minor shifts in interplanar spacing (d (A)) and minorvariation in relative intensity (I/Io) can occur as will be apparent toone of ordinary skill in the art.

                  TABLE I                                                         ______________________________________                                        X-Ray Diffraction Pattern of                                                  NaB.sub.2 Mg.sub.4 Mn.sub.2 O.sub.x                                                   d(A) I/Io                                                             ______________________________________                                                7.7  100                                                                      7.2  1                                                                        5.6  19                                                                       4.6  3                                                                        4.4  10                                                                       4.2  7                                                                        3.6  7                                                                        3.34 15                                                                       3.31 14                                                                       2.99 3                                                                        2.97 2                                                                        2.81 19                                                                       2.77 2                                                                        2.74 10                                                                       2.58 4                                                                        2.49 3                                                                        2.46 53                                                                       2.43 10                                                                       2.39 1                                                                        2.33 1                                                                        2.31 5                                                                ______________________________________                                    

A still more particularly preferred class of catalysts useful in theprocesses of this invention are mixed oxide compositions containing Na,Mg and boron which compositions are characterized by: (1) the presenceof the crystalline compound NaB₂ Mg₄ Mn₂ O_(x) and (2) a stoichiometricexcess in the composition of Mn relative to at least one of the otherelements of the crystalline compound. In this latter regard, astoichiometric excess of Mn relative to boron is preferred. Still morepreferred are excess amounts of Na, Mg and Mn relative to boron. Thus,this more particularly preferred class of catalysts contains additionalredox active material (i.e., additional reducible oxides of Mn). Forexample, such redox active crystalline compounds as Mg₆ MnO₈, MgMn₂ O₄,Na₀.7 MnO₂.05, NaMnO₂, Na₃ MaO₄, etc., may be present in the mixed oxidecomposition.

CATALYST PREPARATION

The boron-promoted reducible metal oxide compositions may be supportedby or diluted with conventional support materials such as silica,alumina, titania, zirconia and the like, and combinations thereof. Whensupports are employed, alkaline earth oxides, especially magnesia, arepreferred.

The catalysts are conveniently prepared by any of the methods associatedwith similar compositions known in the art. Thus, such methods asprecipitation, co-precipitation, impregnation, granulation, spray dryingor dry-mixing can be used. Supported solids may be prepared by methodssuch as adsorption, impregnation, precipitation, co-precipitation, anddry-mixing. Thus, a compound of Mn, Sn, In, Ge, Pb, Sb, Bi, Pr, Tb, Ce,Fe and/or Ru and a compound of boron (and other components) can becombined in any suitable way. Substantially any compound of the recitedcomponents can be employed. Typically, compounds used would be oxides ororganic or inorganic salts of the recited components.

To illustrate, when preparing a catalyst containing: (1) a reduciblemetal oxide componet (e.g., Mn), (2) an alkali metal component, (3) aboron component and (4) an alkaline earth component: one suitable methodof preparation is to impregnate compounds of fourth component of thecomposition with solutions of compounds of Mn, alkali metals, and/orboron. Suitable compounds for impregnation include the acetates, acetylacetonates, oxides, carbides, carbonates, hydroxides, formates,oxalates, nitrates, phosphates, sulfates, sulfides, tartrates,fluorides, chlorides, bromides, or iodides. After impregnation thepreparation is dried to remove solvent and the dried solid is calcinedat a temperature selected within the range of about 300° to 1200° C.Particular calcination temperatures will vary depending on the compoundsemployed.

Preferably, the alkaline earth component is provided as the oxide.Preferably, the alkali metal component is provided as a basiccomposition of the alkali metal(s). Examples are sodium hydroxide,sodium acetate, lithium hydroxide, lithium acetate, etc. When P isemployed as an additive, it has been found desirable to add the alkalimetal and P to the composition as compounds such as the orthophosphates,metaphosphates, and pyrophosphates of alkali metals. Pyrophosphates arepreferred. Sodium pyrophosphate is particularly preferred.

Preferably, the boron component is provided as boric acid, boric oxide(or anhydride), alkali metal borates, boranes, borohydrides, etc.,especially boric acid or oxide.

Formation of the crystalline compound NaB₂ Mg₄ Mn₂ O_(x) may beaccomplished by reacting active compounds of the substituent elements.Suitable compounds of the substituent elements have been described aboveand are illustrated below in the Examples. A suitable mixture of thereactive compounds is formed and heated for a time sufficient to formthe crystalline material. Typically, a temperature of about 850° toabout 950° C. is sufficient. When preparing mixed oxide compositionscharacterized by the presence of the crystalline compound, thecomposition is desirably incorporated with binders of matrix materialssuch as silica, alumina, titania, zirconia, magnesia and the like.

Regardless of which particular catalyst is prepared or how thecomponents are combined, the resulting composite will generally be driedand calcined at elevated temperatures prior to use. Calcination can bedone under air, H₂, carbon oxides, steam, and/or inert gases such as N₂and the noble gases.

HYDROCARBON CONVERSION PROCESS

The catalyst compositions of the present invention are generally usefulfor hydrocarbon conversion processes. Contacting a hydrocarbon food withthe active composition produces hydrocarbon product, coproduct water,and a reduced catalyst composition. The reduced catalyst composition isreadily reoxidized to an active state by contact with an oxidant such asair or other oxygen-containing gases. The process may be effected in acyclic manner wherein the catalyst is contacted alternatively with ahydrocarbon feed and then with an oxygen-containing gas. The process mayalso be effected in a noncyclic manner wherein the catalyst is contactedconcurrently with a hydrocarbon feed and an oxygen-containing gas.Operating conditions are not critical to the use of this invention,although temperatures are generally within the range of about 500° to1000° C. Gas/solid contacting steps may be performed according to any ofthe known techniques: e.g., the solids may be maintained as fixed beds,fluidized beds, moving bed, ebullating beds, etc. Solids may bemaintained in one contact zone or may recirculate between multiplecontact zones (e.g., between oxygen-contact and hydrocarbon-contactzones).

METHANE CONVERSION PROCESS

One more specific application for the compositions of this invention isthe conversion of methane to higher hydrocarbon products. The processcomprises contacting a gas comprising methane with a compositioncomprising a boron-promoted reducible metal oxide to produce higherhydrocarbon products, coproduct water, and a composition comprising areduced metal oxide. In addition to methane, the feedstock may containother hydrocarbon or non-hydrocarbon components, although the methanecontent should typically be within the range of about 40 to 100 volumepercent, preferably about 80 to 100 volume percent, more preferablyabout 90 to 100 volume percent. Operating temperatures are generallywithin the range of about 500° to 1000° C. Although not narrowlycritical in the context of this invention, both total pressure andmethane partial pressures effect results. Preferred operating pressuresare within the range of about 1 to 100 atmospheres, more preferablyabout 1 to 30 atmospheres.

As indicated in the description of hydrocarbon conversion processes, avariety of process embodiments, including various gas/solids-contactingmodes, may be employed.

METHANE CONVERSION PROCESS (COFEED)

In one particular embodiment of the broader methane conversion processesof this invention, methane is contacted with a boron-promoted catalystin the presence of a gaseous oxidant.

The gaseous oxidant is selected from the group consisting of molecularoxygen, oxides of nitrogen, and mixtures thereof. Preferably, thegaseous oxidant is an oxygen-containing gas. A preferredoxygen-containing gas is air. Suitable oxides of nitrogen include N₂ O,NO, N₂ O₃, N₂ O₅ and NO₂. Nitrous oxide (N₂ O) is a presently preferredoxide of nitrogen.

The ratio of hydrocarbon feedstock to gaseous oxidant gas is notnarrowly critical. However, the ratio will desirably be controlled toavoid the formation of gaseous mixtures within the flammable region. Thevolume ratio of hydrocarbon/gaseous oxidant is preferably within therange of about 0.1-100:1, more preferably within the range of about1-50:1. Methane gaseous oxidant feed mixtures containing about 50 to 90volume % methane have been found to comprise a desirable feedstream.

Operating temperatures for this embodiment of the invention aregenerally within the range of about 300° to 1200° C., more preferablywithin the range of about 500° to 1000° C. Best results for contactsolids containing manganese have been found at operating temperatureswithin the range of about 800° to 900° C. If reducible oxides of metalssuch as In, Ge or BI are present in the solid, the particulartemperature selected may depend, in part, on the particular reduciblemetal oxide(s) employed. Thus, reducible oxides of certain metals mayrequire operating temperatures below the upper part of the recited rangeto minimize sublimation or volatilization of the metals (or compoundsthereof) during methane contact. Examples are: (1) reducible oxies ofindium, (operating temperatures will preferably not exceed about 850°C.); (2) reducible oxides of germanium (operating temperatures willpreferably not exceed about 850° C.); and (3) reducible oxides ofbismuth (operating temperatures will preferably not exceed about 850°C.).

Operating pressures for the methane contacting step are not critical.However, both general system pressure and partial pressures of methaneand oxygen have been found to effect overall results. Preferredoperating pressures are within the range of about 0.1 to 30 atmospheres.

The space velocity of the gaseous reaction streams are similarly notcritical, but have been found to effect overall results. Preferred totalgas hourly space velocities are within the range of about 10 to 100,000hr.⁻¹ more preferably within the range of about 600 to 40,000 hr.⁻¹.

Contacting methane and a reducible metal oxide to form higherhydrocarbons from methane also produces coproduct water and reduces themetal oxide. The exact nature of the reduced metal oxides are unknown,and so are referred to as "reduced metal oxides". Regeneration ofreducible metal oxides in this "cofeed" embodiment of the presentinvention occures "in situ"--by contact of the reduced metal oxide withthe gaseous oxidant cofed with methane to the contact zone.

The contact solids may be maintained in the contact zone as fixed,moving, or fluidized beds of solids. A fixed bed of solids is currentlypreferred for this embodiment of the invention.

The effluent from the contact zone contains higher hydrocarbon products(e.g., ethylene, ethane and other light hydrocarbons), carbon oxides,water, unreacted hydrocarbon (e.g., methane) and oxygen, and other gasespresent in the oxygen-containing gas fed to the contact zone. Higherhydrocarbons may be recovered from the effluent and, if desired,subjected to further processing using techniques known to those skilledin the art. Unreacted methane may be recovered and recycled to thecontact zone.

OXIDATIVE DEHYDROGENATION PROCESS

Another more specific application for the compositions of this inventionis the dehydrogenation of dehydrogenatable hydrocarbons. The processcomprises contacting a gas comprising a dehydrogenatable hydrocarbonwith a composition comprising a boron-promoted reducible metal oxide toproduce dehydrogenated hydrocarbon product, coproduct water, and acomposition comprising a reduced metal oxide. Dehydrogenatablehydrocarbons include a wide variety of hydrocarbons: e.g., C₂ + alkanes,cycloalkanes, olefins, alkylaromatics, etc. The dehydrogenated productdepends in part on the feedstock selected. For example, alkanes may bedehydrogenated to form olefins, diolefins, alkynes, etc., and olefinsmay be dehydrogenated to form diolefins, alkynes, etc. One preferredclass of feedstock comprises C₂ -C₅ alkanes (both branched andunbranched). One preferred process embodiment comprises oxidativedehydrogenation of C₂ -C₅ alkanes to form the correspondingmono-olefins.

Operating temperatures are generally within the range of about 500° to1000° C. Operating pressures are not narrowly critical. In general, theprocess is conducted within the parameters of the oxidativedehydrogenation art, but uses a novel catalyst.

EXAMPLES

The invention is further illustrated by reference to the followingexamples. Experimental results reported below include conversions andselectivities calculated on a carbon mole basis. Space velocities arereported as gas hourly space velocities (hour⁻¹) and are identifiedbelow as "GHSV". Methane and methane/air contact runs were made afterthe solids had been heated to reaction temperature in a stream of heatednitrogen.

At the end of each methane contact run, the reactor was flushed withnitrogen and the solids were regenerated under a flow of air (usually at800° C. for 30 minutes). The reactor was then again flushed withnitrogen and the cycle repeated. Results reported below are based onsamples collected after the catalysts had "equilibrated", i.e., afterany aberrant characteristics of freshly prepared catalyst haddissipated.

EXAMPLE 1

A catalyst was prepared by mixing boric acid and manganese (II) acetatein the following mole ratio, 2:3. The mixture was calcined in air at800° C. for 16 hours. When the catalyst was contacted with methane at800° C. and 600 GHSV, the methane conversion was 25% with 27%selectivity of C₂ + hydrocarbon products.

COMPARATIVE EXAMPLE A

When bulk manganese oxide (Mn₂ O₃) was contacted with methane at 800° C.and 860 GHSV, the methane conversion was 30% with 4% selectivity to C₂ +hydrocarbon products.

EXAMPLE 2

A catalyst was prepared by mixing (in a ball mill) manganese dioxide(33.2 grams), boric acid (11.3 grams) and magnesia (42.3 grams) withsufficient water to make a paste. The paste was dried for 4 hours at100° C. and then calcined in air at 900° C. for 16 hours. Table II showsone-minute cumulative results obtained when the catalyst was contactedwith methane.

                  TABLE II                                                        ______________________________________                                                            % Selectivity                                             Temp. (°C.)                                                                      GHSV    % Conversion                                                                              C.sub.2 +                                                                          CO.sub.x                                                                             Coke                                ______________________________________                                        825       1200    30.4        78.6 21.1   0.3                                 825       600     38.1        66.0 33.8   0.2                                 800       600     29.8        76.1 23.7   0.2                                 ______________________________________                                    

When the catalyst was contacted with an equal volume mixture ofmethane/air at 850° C. and a total GHSV of 2400 hr.⁻¹, the methaneconversion obtained was 25% with 72% selectivity to C₂ + hydrocarbonproduct.

EXAMPLE 3

A catalyst was prepared by mixing (in a ball mill) manganese dioxide (33grams), boric acid (11 grams), sodium hydroxide (15 grams) and magnesia(42 grams). This corresponds to an atomic ratio of Na/Mg/Mn/B of about7/12/4/2. The mixture was calcined in air at 900° C. for 16 hours. Thefinished catalyst contained the crystalline compound NaB₂ Mg₆ Mn₂ O_(x),but also contained an amount of Na, Mg, and Mn in excess of thestoichiometric amount. Table III shows two-minute cumulative resultsobtained when the catalyst was contacted with methane.

                  TABLE III                                                       ______________________________________                                                            % Selectivity                                             Temp. (°C.)                                                                      GHSV    % Conversion                                                                              C.sub.2 +                                                                          CO.sub.x                                                                             Coke                                ______________________________________                                        825       1200    34.5        62.2 37.7   0.1                                 850       2400    32.0        60.5 39.5   0.1                                 825       600     75.3        24.8 73.2   2.0                                 800       600     17.0        77.1 22.6   0.3                                 ______________________________________                                    

When the catalyst was contacted with an equal volume mixture ofmethane/air at 850° C. and a total GHSV of 2400 hr.⁻¹, the methaneconversion was 24% with 70% selectivity to C₂ + hydrocarbon products.

EXAMPLE 4

A catalyst was prepared by dry mixing Na₂ B₄ O₇ 10H₂ O (29.8 grams),Mn(C₂ H₃ O₂)₂ 4H₂ O (76.5 grams) and magnesia (25 grams). Thiscorresponds to an atomic ratio of Na/Mg/Mn/B of about 1/4/2/2. Themixture was calcined in air at 940° C. for 16 hours. The finishedcatalyst contained the crystalline compound NaB₂ Mg₆ Mn₂ O_(x) and didnot contain a stoichiometric excess of any of the substituent elements.Table IV shows two-minute cumulative results obtained when the catalystwas contacted with methane.

                  TABLE IV                                                        ______________________________________                                                            % Selectivity                                             Temp. (°C.)                                                                      GHSV    % Conversion                                                                              C.sub.2 +                                                                          CO.sub.x                                                                             Coke                                ______________________________________                                        825       1200    13.0        77.7 21.5   0.8                                 850       600     38.1        66.0 33.8   0.2                                 800       600     29.8        76.1 23.7   0.2                                 ______________________________________                                    

When the catalyst was contacted with an equal volume mixture ofmethane/air at 850° C. and at total GHSV of 2400 hr.⁻¹, the methaneconversion was 28.5% with 69% selectivity to C₂ + hydrocarbon products.

EXAMPLE 5

A catalyst was prepared by ball milling manganese dioxide (32.2 grams),boric acid (11.3 grams), magnesia (42.3 grams) and lithium hydroxide(9.2 grams). The milled mixture was calcined in air at 900° C. for 16hours. Table V shows cumulative results obtained when the catalyst wascontacted with methane at 840° C.

                  TABLE V                                                         ______________________________________                                        Run Length        %           % Selectivity                                   (seconds) GHSV    Conversion  C.sub.2 +                                                                          CO.sub.x                                                                             Coke                                ______________________________________                                        15        1200    36.7        77.5 17.1   5.4                                 15        2400    21.0        92.4 6.6    1.3                                 30        2400    16.2        93.1 5.6    1.2                                 60        1200    25.0        88.2 9.5    2.3                                 ______________________________________                                    

EXAMPLE 6 AND COMPARATIVE EXAMPLE B

A catalyst (Example 6) was prepared by mixing sodium acetate, boricacid, magnesia and ferrous nitrate in the following mole ratio, 1:2:4:2.The mixture was calcined in air at 940° C. for 16 hours. When thecatalyst was contacted with an equal volume mixture of methane/air at850° C. and a total GHSV of 2400 hr.⁻¹, the methane conversion was22.5%with 67% selectivity to C₂ + hydrocarbon products.

A catalyst (Comparative Example B) was prepared as described above inExample 4 except the boron component was omitted. When the catalyst wascontacted with an equal volume mixture of methane/air at 850° C. and atotal GHSV of 2400 hr.⁻¹, the methane conversion was 18.2% with 41.0%selectivity to C₂ + hydrocarbon products.

EXAMPLE 7

A catalyst was prepared by ball milling boric acid (6.7 grams), NaMnO₄3H₂ O (32.7 grams) and magnesia (40.0 grams). This corresponds to anatomic ratio of Na/Mg/Mn/B of about 3/18/3/2. The mixture was calcinedin air at 850° C. for 16 hours. The finished catalyst contained thecrystalline compound NaMg₄ Mn₂ B₂ O_(x) (as exhibited by the x-raydiffraction pattern shown in Table VI), but also contained an amount ofNa, Mg and Mn in excess of the stoichiometric amount.

                  TABLE VI                                                        ______________________________________                                        d(Å) I/Io           d(Å)                                                                             I/Io                                           ______________________________________                                        7.76     100            2.18   3                                              7.18     4              2.12   37                                             5.67     20             2.11   12                                             4.87     9              2.09   4                                              4.61     4              2.05   31                                             4.38     15             2.00   9                                              4.25     9              1.95   18                                             3.59     14             1.87   10                                             3.46     2              1.82   3                                              3.34     30             1.79   3                                              3.31     18             1.76   2                                              3.00     5              1.70   3                                              2.97     4              1.62   5                                              2.82     22             1.59   8                                              2.74     16             1.55   2                                              2.67     6              1.54   15                                             2.58     9              1.51   10                                             2.53     4              1.49   13                                             2.50     7              1.41   7                                              2.45     63             1.39   5                                              2.43     19             1.38   4                                              2.39     2              1.37   3                                              2.33     2              1.36   3                                              2.31     10             1.26   6                                              2.29     15                                                                   2.23     4                                                                    2.21     2                                                                    2.19     2                                                                    ______________________________________                                    

A study of catalyst life was performed according to the cycle, methanecontact/N₂ purge/air regeneration/N₂ purge. Methane contact wasperformed at 1200 GHSV for about one minute. Approximately 5 runs perhour were performed over a period exceeding 7 months. Table VIIsummarizes results obtained.

                  TABLE VII                                                       ______________________________________                                                              % Methane % C.sub.2 +                                   Cycle # Temp. (°C.)                                                                          Conversion                                                                              Selectivity                                   ______________________________________                                        1350    815           18        82                                            4050    815           26        78                                            6750    815           23        78                                            9450    815           26        74                                            12,150  815           24        74                                            14,850  815           20        78                                            17,550  820           26        76                                            20,250  820           24        76                                            22,950  820           23        82                                            27,000  820           26        73                                            ______________________________________                                    

What is claimed:
 1. In an improved method for dehydrogenatingdehydrogenatable hydrocarbons which comprises contacting a gascomprising dehydrogenatable hydrocarbons at oxidative dehydrogenationconditions with a solid comprising at least one oxide of at least onemetal which oxides when contacted with dehydrogenatable hydrocarbons atoxidative dehydrogenation conditions are reduced and producedehydrogenated hydrocarbons and water, the improvement which comprisesconducting the contacting in the presence of a promoting amount of atleast one member of the group consisting of boron and compounds thereof,said solid being substantially free of catalytically effective iron. 2.The method of claim 1 wherein the atomic ratio of the reducible metaloxide component (expressed as the metal) to the boron component(expressed as B) is within the range of about 0.1:1 to about 20:1. 3.The method of claim 1 wherein the atomic ratio of the reducible metaloxide component (expressed as the metal) to the boron component(expressed as B) is within the range of about 0.5:1 to about 5:1.
 4. Themethod of claim 1 wherein the solid comprises reducible metal oxidesselected from the group consisting of reducible oxides of Mn, Sn, In,Ge, Pb, Sb, Bi, Pr, Tb, Ce, Ru and mixtures thereof.
 5. The method ofclaim 1 wherein the solid comprises reducible oxides of Mn.
 6. Themethod of claim 1 wherein the reducible oxide and the boron promoter areassociated with a support material.
 7. The method of claim 1 whereindehydrogenatable hydrocarbons are dehydrogenated to dehydrogenatedhydrocarbon products in a cyclic manner comprising contacting the solidalternately with a gas comprising dehydrogenatable hydrocarbons and witha gaseous oxidant.
 8. The method of claim 7 wherein the solid iscontacted with a gas comprising dehydrogenatable hydrocarbons attemperatures selected within the range of about 500° to about 1000° C.9. The method of claim 1 wherein dehydrogenatable hydrocarbons aredehydrogenated to dehydrogenated hydrocarbon products by contacting thesolid concurrently with a gas comprising dehydrogenatable hydrocarbonsand a gaseous oxidant.
 10. The method of claim 9 wherein said concurrentcontact is conducted at temperatures selected within range of about 500°to about 1000° C.
 11. The method of claim 1 wherein the solid is a mixedoxide composition satisfying the empirical formula:

    MB.sub.b C.sub.c O.sub.x

wherein M is selected from the group consisting of Mn, Sn, In, Ge, Pb,Sb, Bi, Pr, Tb, Ce, Ru and mixtures thereof; B is boron; and C is atleast one alkaline earth metal; and wherein b is within the range ofabout 0.1 to about 10, c is within the range of about 0.1 to about 100,and x is the number of oxygen atoms required by the valence states ofthe other elements.
 12. The method of claim 11 wherein the mixedcomposition comprises reducible oxides of Mn.
 13. The method of claim 11wherein C is Mg.
 14. The method of claim 11 wherein C is Ca.
 15. Themethod of claim 1 wherein the solid is a mixed oxide compositionsatisfying the empirical formula:

    MA.sub.a B.sub.b C.sub.c O.sub.x

wherein M is selected from the group consisting of Mn, Sn, In, Ge, Pb,Sb, Bi, Pr, Tb, Ce, Ru and mixtures thereof; A is at least one alkalimetal; B is boron; C is at least one alkaline earth metal; and wherein ais within the range of about 0.01 to about 10, b is within the range ofabout 0.1 to about 20, c is within the range of about 0.1 to about 100,and x is the number of oxygen atoms required by the valence states ofthe other elements.
 16. The method of claim 15 wherein the mixed oxidecomposition comprises reducible oxides of Mn.
 17. The method of claim 15wherein A is sodium.
 18. The method of claim 15 wherein A is lithium.19. The method of claim 15 wherein C is Mg.
 20. The method of claim 15wherein C is Ca.
 21. The method of claim 1 wherein C₂ -C₅ alkanes aredehydrogenated to form the corresponding mono-olefins.
 22. In animproved method for dehydrogenating dehydrogenatable hydrocarbons whichcomprises contacting a gas comprising dehydrogenatable hydrocarbons at atemperature within the range of about 500° to about 1000° C. with asolid comprising at least one oxide of at least one metal which oxideswhen contacted with dehydrogenatable hydrocarbons are reduced andproduce dehydrogenated hydrocarbons and water, the improvement whichcomprises conducting the contacting in the presence of:(a) at least onemember of the group consisting of Li and compounds thereof, (b) at leastone member selected from the group consisting of boron and compoundsthereof, and (c) at least one member of the group consisting of alkalineearth metals and compounds thereof.
 23. The method of claim 22 whereinthe solid is a mixed oxide composition satisfying the empirical formula:

    MLi.sub.a B.sub.b C.sub.c O.sub.x

wherein M is selected from the group consisting of Mn, Sn, In, Ge, Pb,Sb, Bi, Pr, Tb, Ce, Fe, Ru and mixtures thereof; B is boron; C is atleast one alkaline earth metal; and wherein a is within the range ofabout 0.01 to about 10, b is within the range of about 0.1 to about 20,c is within the range of about 0.1 to about 100, and x is the number ofoxygen atoms required by the valence states of the other elements. 24.The method of claim 23 wherein b is within the range of about 0.1 toabout
 10. 25. The method of claim 23 wherein c is within the range ofabout 1 to about
 7. 26. The method of claim 23 wherein the mixed oxidecomposition comprises reducible oxides of Mn.
 27. The method of claim 23C is Mg.
 28. The method of claim 23 C is Ca.
 29. A method fordehydrogenating dehydrogenatable hydrocarbons to form dehydrogenatedproducts which comprises contacting at a temperature within the range ofabout 500 to about 1000° C. a gas comprising dehydrogenatablehydrocarbons with a mixed oxide composition containing Mn, Na, B and Mgwhich composition is characterized by the presence of the crystallinecompound NaB₂ Mg₄ Mn₂ O_(x).
 30. The method of claim 29 wherein themixed oxide composition is further characterized by an amount of Mn inthe composition in excess of the stoichiometric amount of Mn relative toat least one of the other elements of said crystalline compound.
 31. Themethod of claim 30 wherein a stoichiometric excess of Mn relative toboron is provided.
 32. The method of claim 31 wherein the mixed oxidecomposition contains excess amounts of Na, Mg and Mn relative to theamounts required by the amount of boron present to satisfy thestoichiometry of said crystalline compound.
 33. In an improvedhydrocarbon conversion process which comprises contacting a hydrocarbonfeedstock with a solid comprising a reducible metal oxide and which ischaracterized by the production of hydrocarbon product, coproduct water,and a reduced metal oxide, the improvement which comprises conductingthe contacting in the presence of a promoting amount of at least onemember of the group consisting of boron and compounds thereof, saidsolid being substantially free of catalytically effective iron.
 34. Inan improved hydrocarbon conversion process which comprises contacting ahydrocarbon feedstock with a solid comprising a reducible oxide of Mnand which is characterized by the production of hydrocarbon product,coproduct water, and a reduced oxide of Mn, the improvement whichcomprises conducting the contacting with a mixed oxide compositioncontaining Mn, Na, B and Mg and the mixed oxide composition ischaracterized by the presence of the crystalline compound NaB₂ Mg₄ Mn₂O_(x).
 35. The method of claim 34 wherein the mixed oxide composition isfurther characterized by an amount of Mn in the composition in excess ofthe stoichiometric amount of Mn relative to at least one of the otherelements of said crystalline compound.
 36. The method of claim 35wherein a stoichiometric excess of Mn relative to boron is provided. 37.The method of claim 36 wherein the mixed oxide composition containsexcess amounts of Na, Mg and Mn relative to the amounts required by theamount of boron present to satisfy the stoichiometry of said crystallinecompound.